The present invention relates to a process for recovering scrap plastic compounds. In particular, this invention relates to a process for recovering certain thermosetting types of plastic compounds by first hot granulating then forming a fine powder of the compound. More specifically, the present invention relates to a process for recovery of scrap crosslinkable polyethylene compounds in a useable form.
As is well known, in the processing of plastic compounds such as molding, extrusion, and the like, certain portions of the compound end up as scrap compound either in the form of rejected articles, or sprues and runners of a molding process or, in the case of most extrusion processes, as bleed from the extruder upon starting-up or shutting down. Also often large quantities of virgin material must be scrapped because it was compounded incorrectly or otherwise does not meet the specifications required for a particular use.
Industry has long recognized the value of this scrap but the issue has recently taken on new significance now that world supplies of feedstock petrochemicals are in short supply, thereby substantially raising the prices of new compound, and because of ecological pressures which now restrict the previous common means of disposal, i.e., incineration or landfill. It is also now more important to conserve the energy values represented by plastic compounds by reusing as much scrap as possible but not only as an inert filler but more desirably as a direct replacement for some of the virgin material.
Industry has generally risen to the challenge and developed various techniques to reuse some types of plastic compounds. For example, some thermoplastic types of plastic compounds can be reused simply by granulating the scrap since granules of this type of compound soften and become semi-liquid when heated during reuse so that a new and useful article can be formed by molding or extrusion or the like.
Other, more exotic, methods such as solvent recovery, have been developed for the recovery of certain specific compounds but prior art has not developed a simple and inexpensive method for reclaiming thermosetting plastic compounds. This problem remains because of the very nature of thermosetting compounds in which the application of heat during processing causes the compound to cure and become harder (i.e., "set"). Therefore attempts to simply granulate then remold a thermosetting compound have generally resulted in ineffective performance, sometimes even producing a mass of granules with little coheasion.